JP2009517876A - Photocell - Google Patents

Abstract

The present invention relates to a photovoltaic cell comprising at least one first junction between a pair of semiconductive regions (4-9). At least one of the pair of semiconductor regions includes at least a portion of a superlattice including a first material having a formation of a second material spaced apart therein. Since the formation has a sufficiently small dimension, the effective band gap of the superlattice is at least partially determined by the dimension. An absorbing layer is applied between the semiconducting regions, the absorbing layer including a material for absorbing radiation and causing excitation of charge carriers, the absorbing layer having an excitation level by the material itself. It has a thickness as determined. At least one of the effective energy bands of the superlattice and one of the excitation levels of the material of the absorption layer are respectively at least one of the excitation levels of the material of the absorption layer and the effective energy of the superlattice Selected to match the band.
[Selection] Figure 1

Description

The present invention relates to a photovoltaic cell comprising at least one first junction between a pair of semiconducting regions, wherein at least one of the pair of semiconducting regions is of a second substance. The superlattice includes at least a portion of a superlattice that includes a first material with a formation spaced apart therein, and the formation has a sufficiently small dimension so that the superlattice The effective band gap is determined at least in part by the dimensions, an absorption layer is applied between the semiconductive regions, and the absorption layer includes a material for absorbing radiation and providing charge carrier excitation. The absorption layer has such a thickness that the excitation level is determined by the substance itself.

The invention also relates to a method of manufacturing an array of photovoltaic cells.

The invention also relates to a photovoltaic device comprising a plurality of photovoltaic cells.

Examples of such photovoltaic cells, manufacturing methods and photovoltaic devices are known. U.S. Patent No. 6,057,049 describes a pin type photovoltaic cell that includes a transparent substrate made of glass or plastic and covered with a layer of transparent conductive oxide. A p-layer is formed on the conductive oxide layer and an intrinsic layer (i-layer) is formed on the p-layer. An n-layer is formed on the i-layer and a metal back contact layer is formed on the n-layer. In order to reduce absorption in the doped layer without reducing the conductivity of the doped layer, a superlattice is used to form p-layers and / or n-layers.

Patent Document 2 includes a first active region including a superlattice material having a band gap having a first predetermined value, and a second superlattice material having a band gap having a second predetermined value. Described is a tandem solar cell including a second active region and means for electrically interconnecting the first and second active regions such that current can flow between the first and second active regions is doing. Amorphous superlattices are multi-layered materials, and these layers are thin plates of semi-conductive or insulating tetrahedrally bonded amorphous materials, which are tetrahedrally bonded elements or tetrahedrally bonded elements It is formed from an alloy containing elements. Each layer is less than about 1500 mm thick.

The problem with the latter battery is that in order to make it sufficiently efficient, it must contain numerous combinations of different semiconducting material layers that form the active region. is there. Otherwise, only a small part of the incident light will be absorbed in the active region formed by the superlattice. However, adding additional layers to the superlattice would make it expensive to manufacture the known device.
US Pat. No. 4,718,947 U.S. Pat. No. 4,598,164

It is an object of the present invention to provide a photovoltaic cell, a manufacturing method, and a photovoltaic device that provide solar energy conversion with relatively high efficiency for a given manufacturing effort.

At least one of the effective energy bands of the superlattice and one of the energy excitation levels of the material of the absorption layer are respectively at least one of the energy excitation levels of the material of the absorption layer and the effective energy of the superlattice. This object is achieved by a photovoltaic cell characterized in that it is selected to substantially match the band.

Since at least one first of the two semiconductive regions includes at least a portion of the superlattice, the photovoltaic cell can be made relatively efficient. The effective band gap of the superlattice can be matched to a convenient range of the solar spectrum. The disadvantage (and sufficient) that the dimensions of the formation of both materials must be small enough to give the superlattice an effective bandgap that differs from the effective bandgap of any semiconductor material in the individual layers of the superlattice. In order to build a photovoltaic cell that absorbs radiant radiation, the disadvantage that usually many layers must be deposited is reduced because there is a layer of material to absorb the radiation and cause excitation of the charge carriers . Excited charge carriers are moved to adjacent superlattices, thus increasing the efficiency of solar energy conversion.

Within the photovoltaic cell, the ability to absorb excited radiation and generate excited charge carriers, followed by the opposite polarity charge carriers are separated (due to the presence of p-type and n-type doped layers, the opposing charges are incorporated A distinction can be made between the function, the function of transporting charge carriers, and the function of collecting separated and transported charge carriers. The advantage of the proposed structure is that functional separation can be achieved and further optimized. The material of the absorption layer for the absorption of radiation can be specifically selected to have a high absorption coefficient, while the dimensions of the first and second materials forming the superlattice, and the formation of both materials Are selected to provide the desired effective band gap. The effective band gap depends on both the chemical and / or structural composition of the material in the superlattice and the dimensions of the material's formation. The absorption layer for absorbing radiation is uniform and allows formation in one processing step, the excitation level of the layer being independent of the thickness of the layer. The excited level depends only on the chemical composition of the absorbing layer and / or the phase of its components.

When the excitation level of the absorption layer for absorbing radiation substantially matches the effective conduction band, the movement of negative charge carriers is more efficient. Less energy is lost after movement when the levels are matched, for example, within 0.2 eV of the lower edge of the effective conduction band, more preferably within 0.1 eV. If the material of the absorbing layer for absorbing radiation exhibits at least one stable energy level substantially matching the effective valence band of the semiconducting region adjacent to the absorbing layer, The movement of charge carriers is more efficient. When the level matches within 0.2 eV of the upper edge of the effective valence band, more preferably within 0.1 eV, less energy is lost after movement. In other words, at least one of the effective bands of the superlattice and one of the excitation levels of the material of the absorption layer are substantially substituting into at least one of the excitation levels of the material of the absorption layer and the effective band of the superlattice, respectively. Choosing to match consistently increases the efficiency of the photovoltaic cell. A semiconducting region containing at least a portion of the superlattice functions as an energy selective transport layer to remove carriers generated in the absorbing layer for absorbing radiation.

One embodiment includes a series of semiconductive region pairs separated by a junction and having an effective band gap that decreases with each pair, wherein at least two of the semiconductive regions are superlattices and An absorption layer of a material adjacent to it for absorbing radiation and resulting in excitation of charge carriers, the absorption layer having a thickness such that the excitation level is determined by the material itself, Yes.

In this way, so-called tandem batteries or multi-junction batteries are provided. The advantage of this configuration is that it can be used to convert different ranges of the solar spectrum in different regions specifically adapted to the respective ranges. This reduces heat generation when charge carriers are generated by charge carrier thermalization, i.e. absorption of photons having an energy higher than the effective band gap of the region in which the photons are absorbed. An absorption layer of a material directly adjacent to a series of superlattices and having a thickness such that the excitation level is determined by the material itself for absorbing radiation and causing excitation of charge carriers. The presence ensures that the maximum possible frequency range is filtered before the radiation reaches the next semiconductive region in the series.

In one embodiment, each superlattice includes a periodically repeated combination of layers of different semiconductor materials, the layers being sufficiently thin that the effective band of any semiconductor material in the individual superlattice layers. An effective band gap different from the gap is given to the superlattice.

Compared to other embodiments, such as embodiments having quantum dot superlattices, the embodiments of the present invention have the advantage that there is a clear path for manufacturing such superlattices on an industrial scale.

In one embodiment, the absorber layer is sandwiched between semiconductive regions, which have different effective band gaps.

This embodiment allows charge carriers generated on both sides of the absorbing layer to contribute to the efficiency of the photovoltaic cell.

In one embodiment, the material for absorbing radiation includes at least one of a direct transition semiconductor, an organic molecular material, and a material including nanocrystals.

The latter type of material includes materials that contain a multiphase structure, for example, materials that consist of a matrix having nanometer-sized particles regularly arranged in the material. In these materials, the absorption edge can be manipulated by changing the size of the particles and can therefore be energetically matched to the effective band gap of the adjacent superlattice. This contributes to making the photovoltaic cell relatively efficient. Organic molecular materials are most easily adaptable to achieve absorption in a specific range of the solar spectrum, and are best adapted to match the effective conduction band and / or valence band of a specific superlattice. Easy.

In one embodiment, the superlattice includes a periodically repeated combination of layers of different amorphous semiconductor materials.

The above effect is to avoid any distortion due to lattice mismatch substantially. For this reason, amorphous semiconductor materials are easiest to stack.

In one embodiment, the superlattice includes a periodically repeated combination of layers of hydrogenated semiconductor material.

The above effect is to passivate coordination defects.

According to another aspect, a method of manufacturing an array of photovoltaic cells includes depositing a layer of material over the entire length of the foil and patterning at least one of the layers to form an array of photovoltaic cells, thereby An array of batteries according to the present invention is formed.

Because of the construction of the photovoltaic cell of the present invention, fewer layers of material need to be deposited resulting in substantial savings in manufacturing effort.

Preferably, the layer is deposited at at least one station in the production line, where a quasi-continuous length of foil is advanced through each station.

This is a convenient way to produce an array of photovoltaic cells. This is because the desired array can be separated from the foil. Moreover, time-consuming chamber conditioning is avoided and the exchange time between the deposition of the layer of material is omitted from the total time for manufacturing the array.

According to another aspect, a photovoltaic device according to the present invention includes a plurality of photovoltaic cells according to the present invention.

The device is relatively easy to manufacture and at the same time exhibits good energy conversion efficiency.

The present invention will now be described in further detail with reference to the accompanying drawings.

A photovoltaic cell 1 is shown in FIG. 1 only to the extent necessary to illustrate the invention. In an actual photovoltaic device, the photovoltaic cell 1 will be encapsulated in one or more layers of plastic foil and / or additional layers including glass sheets to seal the photovoltaic cell from the environment. In the illustrated embodiment, the photovoltaic cell 1 is a tandem battery, ie a stack of single cells. In this case, the individual cells in the stack are electrically connected in series. Parallel connection is an alternative, but more complex.

The illustrated photovoltaic cell 1 is a two-terminal device, and includes an upper electrode 2 and a lower electrode 3. The upper electrode is made of a transparent conductive material such as SnO ₂ (tin oxide), ITO (indium tin oxide), ZnO (zinc oxide), Zn ₂ SnO ₄ (zinc stannate), Cd ₂ SnO ₄ (cadmium stannate) or InTiO (Made of indium titanium oxide). The lower electrode 3 is made at least partly from a metal, for example Al (aluminum) or Ag (silver), a metal alloy or a transparent conductive material. In one embodiment, the lower electrode 3 is made of a combination of a metal and a transparent conductive material, the former being placed towards the outside of the photovoltaic cell 1.

The photovoltaic cell 1 in the embodiment of FIG. 1 includes semiconductive regions 4-9. In other embodiments, there may be fewer or more such regions. Of each pair of semiconducting regions, one is arranged to function as an efficient transport region for electrons and the other as an efficient transport region for holes.

In the embodiment of FIG. 1, each of the semiconductive regions 4-9 includes a superlattice. Semiconductors based on superlattices are known in the prior art. As used herein, the term superlattice includes both of the two known variations, i.e., a layer of a first material having a layer of a second material spaced apart therein, Both a deformation that is both thin enough to affect the band gap, and a deformation in which the nanocrystal is formed from a semiconducting layer and the size of the nanocrystal, ie quantum dot, affects the effective band gap of the superlattice Used to represent Examples of the latter type of superlattice are described in Green, M .; A. , "Silicon nanostructures for all-silicon tandem solar cells", 19th European Photovoltaic Solar Energy Conference and Exhibition, French, 7th, 2004, 6th, 2004 Layered types of superlattices are included in the more detailed embodiments described herein.

A layered superlattice includes a periodically repeated combination of a layer of a low bandgap semiconductor material called a well and a layer of a wide bandgap material called a barrier. Accordingly, in FIG. 1, the first semiconductive region 4 includes a repeated combination of the first barrier layers 10a to 10c and the first well layers 11a to 11c. The second semiconductive region 5 includes repeated combinations of the second barrier layers 12a-12c and the second well layers 13a-13c, while the third semiconductive region 6 It includes a repeated combination of the third barrier layers 14a-14c and the third well layers 15a-15c. The fourth, fifth and sixth semiconductive regions 7-9 are respectively the fourth, fifth and sixth barrier layers 16a-16c, 17a-17c and 18a-18c, respectively, the fourth, fifth and The sixth well layers 19a to 19c, 20a to 20c, and 21a to 21c are alternately included. The thickness values of the layers 10 to 21 are in the range of 1-2 nm and at least in the range of less than 10 nm. Each of the semiconductive regions 4-9 has a total thickness of the order of one hundred nm, at least less than 200 nm.

The layers 10-21 of the embodiment of FIG. 1 are made from a hydrogenated or fluorinated amorphous semiconductive material. Suitable examples are hydrogenated amorphous silicon (a-Si: H), hydrogenated amorphous silicon germanium (a-SiGe: H), hydrogenated amorphous silicon carbide (a-SiC: H), hydrogenated amorphous silicon nitride (a -SiN: H) and hydrogenated amorphous silicon oxide (a-SiO: H). The band gap of a-Si: H depends on the deposition conditions and varies from 1.6 eV to 1.9 eV. When a-Si: H is alloyed with carbon, oxygen or nitrogen, the band gap of the alloy widens, while when germanium is added, the band gap decreases. a-Si: H and a-SiGe: H are used as materials for the well, ie well layers 11, 13, 15, 19, 21 and a-SiC: H, a-SiN: H or a-SiO: H Can be used as a material for the barrier, ie barrier layers 10, 12, 14, 16, 18; The aperiodic structure of layers based on a-Si: H and the ability of hydrogen to passivate coordination defects removes the stringent requirements for lattice matching that applies in the case of crystalline superlattices.

One or more of several techniques can be used to form a superlattice. These techniques include chemical vapor deposition, reactive (co) sputtering and reactive (co) evaporation. A convenient technique for producing the illustrated embodiment is plasma enhanced chemical vapor deposition (PECVD). This approach is advantageous because a-Si: H alloying can be easily achieved by adding a suitable gas to a silicon source carrier gas such as silane. It has been demonstrated that superlattices can be fabricated that have interfaces that are neither lattice matched nor epitaxial, but still essentially free of defects and almost steep in atoms.

Separate pairs of adjacent semiconductive regions 4-9 are separated by tunnel recombination junctions 22, 23 that include N-type and P-type regions. The tunnel recombination junctions 22, 23 provide an internal series connection, where recombination of opposite charge carriers arriving from adjacent pairs of semiconductive regions occurs. The tunneling of carriers through the layers forming the tunnel recombination junction facilitates the recombination. Effective recombination of photogenerated carriers occurs through defect states in the center of the junction. The recombination of photogenerated carriers at the center of the junction keeps the current flow in the solar cell.

Of each pair of semiconductive regions, one functions as an efficient transport region for holes and the other functions as an efficient transport region for electrons. In the illustrated embodiment of FIG. 1, superlattices are deposited in N-type and P-type semiconductor regions, ie, doped semiconductor regions that form part of the tunnel recombination junctions 22,23. It is noted that the doped region may include a superlattice.

As is well known, space charges in otherwise doped semiconductors formed by the outdiffusion of most charge carriers from the doped layer produce an internal electric field. This causes separation of mobile charge carriers generated by excitation. The combination of the first and second semiconductive regions 4, 5 converts solar energy within the first range of the solar spectrum, and the combination of the third and fourth semiconductive regions 6, 7 The second, different but possibly overlapping region of the spectrum is transformed, and the combination of the fifth and sixth semiconducting regions 8, 9 transforms yet another range. The tunnel recombination junctions 22, 23 ensure that the three pairs of semiconductive regions are electrically connected in series.

The semiconductive regions 4-9 have an effective band gap that gradually decreases. Thus, the first and second semiconducting regions 4, 5 have a larger effective band gap and consequently capture photons in the higher (frequency) range of the solar spectrum. The middle semiconductive regions 6, 7 have an effective band gap in the middle range of the solar spectrum. The lower semiconductive regions 8, 9 have an effective band gap in the lower range of the solar spectrum. The upper semiconductive regions 4 and 5 are placed closest to the upper electrode 2. In use, the upper electrode 2 is exposed to incident light, and the incident light thus passes through the semiconductive regions 4-9 in order of decreasing effective band gap. This arrangement provides improved efficiency of solar energy conversion because charge carrier thermalization is suppressed.

As a result of inserting first, second and third absorption layers 24 to 26 of material for absorbing radiation in the middle of the upper, middle and lower pairs of semiconductive regions 4 to 9, respectively, incident radiation Most of the absorption of is taken up by the absorption layer. Thus, by reducing the amount of well layers and barrier layers, the thickness of the semiconductive region can be limited, which is advantageous from a manufacturing standpoint. Absorbing layers 24-26 of material for absorbing radiation are adjacent to each superlattice forming a pair. The absorption layer has such a thickness that the excitation level is determined by these compositions. A suitable value for the thickness is in the range of about 50 nm, preferably in the range of about 10 nm.

The absorption layers 24 to 26 may include a direct transition type semiconductor material. Such materials have a relatively high absorption coefficient of 10 ⁴ to 10 ⁶ cm ⁻¹ , so that the absorption layers 24 to 26 can be kept thin. For example, CdS having a band gap of 2.45 eV has an absorption coefficient of about 10 ⁵ cm ⁻¹ at 500 nm, and Cu (In, Ga) (Se, S) ₂ has a band gap of 1.0˜ It can vary over a wide range of 1.7 eV and has an absorption coefficient of 10 ⁴ to 10 ⁵ cm ⁻¹ in this energy range. Absorption involves the excitation of electrons from the valence band to the conduction band. A relatively high absorption coefficient is also an option, i.e. a characteristic of organic molecular substances. Such materials are used in the examples described herein. In organic molecular materials, excited charge carriers are commonly referred to as excitons. Suitable organic molecular materials include porphyrins and phthalocyanines. They have narrow absorption bands centered at frequencies corresponding to photon energy levels of about 2.9 eV and 1.77 eV, respectively. In particular, phthalocyanine molecules are chemically very stable and can be deposited by vacuum evaporation. The excited levels of the material in the absorbing layers 24-26 are selected so that they are allowed to match the effective band of the adjacent superlattice. Since these band gaps can be engineered with the dimensions of the thin layers 10-21, such alignment can be achieved with relatively high accuracy.

The charge carriers in the absorption layers 24 to 26 are excited to a level above the lower boundary of the effective conduction band of the adjacent superlattice. This allows charge carriers to move to the superlattice with relatively high efficiency. The efficiency is high because of the low heat loss that is incurred when charge carriers are moved to the conduction band. The alignment is preferably precise to a value within a tenth of one electron volt, for example a value of 0.1 or 0.2 eV. In molecular material, charge carriers are excited to the lowest unoccupied molecular orbital (LUMO), which is therefore aligned with the lower boundary of the effective conduction band of the adjacent superlattice. Preferably, the state from which the charge carriers are excited (this state is called the highest occupied molecular orbital (HOMO) in the molecular material for absorbing radiation) is at least in the effective valence band. Matches the upper limit to the same accuracy.

FIG. 2 shows the general concept of the photovoltaic cell 1 with an energy diagram. The first and second absorption layers 27 and 28 are adjacent to a part of the superlattices 29 to 32. The superlattices 29 to 32 have substantially the characteristics of an intrinsic semiconductive material. These form an energy selective transport layer having a conduction band or a valence band that is substantially matched to the stable or excited levels of the adjacent absorbing layers 27, 28. In fact, as shown in FIG. 2, the conduction band of the superlattices 30 and 32 is slightly below the excitation level of the adjacent absorption layers 27 and 28, while the valence band of the superlattices 29 and 31. Is slightly above the stable level of the adjacent absorption layers 27, 28.

A part of the superlattice 30 adjacent to the first absorption layer 27 and a part of the superlattice 31 adjacent to the second absorption layer 28 form semiconductive regions having different effective band gaps. Whether a part of one of the superlattices 29 to 32 functions as an effective transport of electrons or holes depends on whether one of the three tunnel recombination junctions 33 to 35 is adjacent to the semiconductive region. Determined by nature. Each of the tunnel recombination junctions 33 to 35 includes a pair of semiconductive layers, one of which is doped into a P-type semiconductive layer and the other is an N-type semiconductive layer. The function of the tunnel recombination junction is to provide a series connection between each of the superlattices 29-32 and the absorbing layers 27, 28 integrated and to construct an internal electric field in the active region of the photovoltaic cell 1. is there.

FIG. 3 shows a variation of the general concept of FIG. Also in this case, the first and second absorption layers 27 and 28 are adjacent to a part of the superlattices 29 to 32. However, the single pair of superlattices 29-32 are different in the embodiment of FIG. The superlattices 29 to 32 are selected so as to have different effective band gaps within the pair. Negative charge carriers excited in the superlattice 29 are forced towards the tunnel recombination junction 34, while positive charge carriers excited in the superlattice 30 are forced into the tunnel recombination junction. The band gap is designed to be sent towards 33.

FIG. 4 shows a production line 36 for producing an array of solar cells having the configuration of the solar cell 1 described so far. The production line 36 in this embodiment includes two stations 37-38 through which the entire length of the foil is advanced. As the foil is moved from the first roll 39 to the second roll 40, an array of solar cells is formed on the foil. The two stations 37, 38 can be more than these and are for illustration only. Solar cells are very efficient by forming layers 10-21, 24-26 one after another at one or more stations 37, 38 placed along the path of the foil, especially when PECVD is used. Can be manufactured automatically. Patterning is applied using laser or other cutting techniques to form individual cells. Because of the use of the first and second rolls 38, 39, quasi-continuous production is possible, limited primarily by the maximum possible diameter of the rolls 39, 40. After further processing, such as application of a plastic protective layer, removal of the backing layer, etc., an array of suitable sizes can be formed from the entire length of the foil. The array is then incorporated into a photovoltaic device containing appropriate connectors and optional additional circuitry. Using a unit of the material in combination with a superlattice with an effective band gap designed to match the absorption band of the spectrally selective absorbing material, especially for use in tandem battery construction, Making the electrical device highly efficient and making it relatively uncomplicated.

The invention is not limited to the embodiments described above but may vary within the scope of the appended claims. For example, the absorption bands of materials for absorbing radiation can partially overlap. Also, one of each pair of semiconducting regions adjacent to a layer for spectrally absorbing radiation is not directly superlattice, but instead of an inorganic, direct transition or indirect transition half. Embodiments made from conductive materials are also possible. Further, the pair of semiconductive regions forming the multi-junction battery may be separated by a layer of inorganic semiconductive material, or such a layer may be applied between the electrode and the superlattice. .

It is the schematic which is not the exact scale which shows the structure of the Example of a photovoltaic cell. It is an energy diagram which shows one deformation | transformation of a photovoltaic cell. It is an energy diagram which shows another modification of a photovoltaic cell. It is the schematic which shows the manufacturing line for manufacturing the array of a photovoltaic cell.

Claims (11)

A photovoltaic cell comprising at least one first junction between a pair of semiconductive regions (4-9), wherein at least one of the pair of semiconductive regions is of a second material Including at least a portion of a superlattice including a first material having a formation spaced apart therein, the formation comprising an effective energy band between the effective energy bands of the superlattice. Having a dimension that is sufficiently small so that a band gap is determined at least in part by the dimensions of the molding, and an absorption layer (24-26) is provided between the semiconductive regions, the absorption layer comprising radiation A photovoltaic cell having a thickness such that an excitation level is determined by the substance itself,
At least one of the effective energy bands of the superlattice and one of the excitation levels of the material of the absorption layer are at least one of the excitation levels of the material of the absorption layer and the superlattice, respectively. A photovoltaic cell selected to match the effective energy band of Comprising a series of pairs of semiconducting regions (4-9) separated by a junction and having an effective band gap that decreases with each pair, wherein at least two of the semiconducting regions (4-9) are super A lattice and a layer of material (24-26) adjacent to it for absorbing radiation and causing charge carrier excitation, having a thickness such that the excitation level is determined by the material itself The photovoltaic cell according to claim 1, comprising: (24-26). Each superlattice includes a periodically repeated combination of layers (10-21) of different semiconductor materials, and has an effective bandgap that is different from the effective bandgap of any semiconductor material in the individual layers of the superlattice. Photovoltaic cell according to claim 1 or 2, wherein the layer is thin enough to be applied to the superlattice. The superlattice is composed of an intrinsic semiconducting material, and the photovoltaic cell further includes at least a pair of separately doped N-type and P-type semiconducting regions arranged to generate an internal electric field within the photovoltaic cell. The photovoltaic cell according to any one of claims 1 to 3. The photovoltaic cell according to claim 1, wherein an absorption layer is sandwiched between the semiconductive regions, and the semiconductive regions have different effective band gaps. The photovoltaic cell according to claim 1, wherein the substance for absorbing radiation contains at least one of a substance containing a direct semiconductor, an organic molecular substance and a nanocrystal. Photovoltaic cell according to any one of the preceding claims, wherein the superlattice comprises a periodically repeated combination of layers (10-21) of different amorphous semiconductor materials. Photovoltaic cell according to any one of the preceding claims, wherein the superlattice comprises a periodically repeated combination of layers (10-21) of hydrogenated semiconductor material. Depositing a layer of material (10-26) over a length of foil and patterning at least some of the layers to form an array of photovoltaic cells (1), thereby comprising A method of manufacturing an array of photovoltaic cells, wherein an array of cells according to any one of 8 is formed. The layer is deposited at at least one of the stations (19, 20) in the production line (18) and a semi-continuous length of foil is advanced through each station (19, 20). How to follow. Photovoltaic device comprising a plurality of photovoltaic cells (1) according to any one of claims 1-8.

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